According to the adaptive array technology, a beam can be directed to a user of a desired wave (beam forming) and a null can be directed to a user of an interference wave (null steering), by appropriately setting weight of each antenna element of an array antenna.
Space-Division Multiple Access (SDMA) scheme has been known, as a multiplexing scheme that utilizes the adaptive array technology. In a mobile communication system that employs the SDMA, a base station device can communicate with each of multiple mobile station devices spatially separated from one another at the same timing by using a common frequency.
As a weight calculation algorithm that calculates weight of each antenna element of an array antenna, there is a weight calculation algorithm that directs a beam to the arriving direction of a known reference signal as well as directs a null to the arriving direction of a signal having low correlation with the reference signal. Besides, there is also a weight calculation algorithm that directs a null to any direction.
In general, when a radio signal is received with an array antenna, the more the number of antenna elements is, the better the receiving quality is. This is because, in array antennas, as the number of antenna elements increases, degrees of freedom in array weight calculation increase, thus making it possible to cope with a complicated propagation environment.
In array antennas, radio signals are received utilizing a predetermined adaptation algorithm. There are various kinds of adaptation algorithms. As a typical adaptation algorithm, there are an adaptation algorithm that optimizes reception of a desired wave by utilizing a known signal (herein referred to as a desired wave optimizing type adaptation algorithm) and an adaptation algorithm that suppresses a spatial component forming a receiving wave depending on its power (herein referred to as a spatial component suppressing type adaptation algorithm).
A specific example of the desired wave optimizing type adaptation algorithm includes MMSE (Minimum Mean Square Error). In addition, a specific example of the spatial component suppressing type adaptation algorithm includes PI (Power Inversion).
Meanwhile, Japanese Patent Application Publication No. 09-205316 discloses a technique in which multiple desired wave optimizing type adaptation algorithms are used while being switched.
In addition, in a diversity technology that is a technology designed to improve communication characteristics, a transmitting side transmits the same data pieces through multiple different communication channels. A receiving side selects or synthesizes received signals received through the multiple communication channels.
A diversity technology that uses different carrier frequencies is referred to as frequency diversity. Meanwhile, a diversity technology that uses different time division slots (hereinafter simply referred to as slots) according to Time Division Multiple Access/Time Division Duplication (TDMA/TDD) scheme is referred to as slot diversity.
Heretofore, there is disclosed a radio communication device that further improves communication characteristics by using the adaptive array technology in addition to the diversity technology (Japanese Patent No. 3579363, for example). However, a gain improvement function and an interference suppression function of the adaptive array technology are in a trade-off relationship with each other. If a priority is given to gain improvement, the effect of interference suppression is reduced, while if a priority is given to interference wave suppression, the gain is reduced. In essence, the gain improvement effect and the interference suppression effect cannot be achieved simultaneously.
Meanwhile, Japanese Patent Application Publication No. 2001-127681 discloses a technique related to an adaptive array base station, which diversity-transmits notification data or paging data so that peak transmission patterns of multiple different emission patterns may have a shape close to omni. This technique is a technique for improving a connection rate of incoming calls of mobile stations, and not a technique for improving communication characteristics by the gain improvement function or the interference suppression function of the adaptive array technology.